Kevin Pietersen may have jeopardised his place in England's squad for next week's third Test against South Africa at Lord's, which will be announced on Sunday morning, by sending texts to his friends and compatriots in the opposition team during the second Test at Headingley.

The selectors convened at Edgbaston on Friday and their chairman, Geoff Miller, stressed that the overwhelming priority remained to provide the team director, Andy Flower, and captain, Andrew Strauss, with the players best equipped to secure the win that England need to square the series and retain their position at the top of the official world Test rankings.

But officials at the England and Wales Cricket Board are still trying to find out the contents of the texts that Pietersen sent at Headingley. Dr Mohammed Moosajee, South Africa's tour manager, confirmed their existence but described them as "friendly banter" – whereas in South Africa's weekly Mail and Guardian newspaper, they were said to contain "less than flattering comments concerning his captain and team-mates".

If the latter description turns out to be true, that could easily prove the final straw in Pietersen's increasingly frayed relationship with virtually everybody else in the England set-up. Disloyalty to his captain and colleagues would be seen as an ultimate betrayal of the team spirit which Strauss and Flower have worked so hard to forge.

However England will also be wary of falling into a trap set by the South Africans. Despite the tourists' official line, that they are "doing their best to stay out of the mess", the creation of further Pietersen-related problems for Flower and Strauss would suit them perfectly in their quest to displace England from the top of the world rankings.

Pietersen has played in 88 of England's last 91 Tests since he made his debut at the start of the 2005 Ashes series at Lord's, when he was preferred to Graham Thorpe in the middle order. This is the first time since then that there has been the slightest doubt over his name appearing in the squad. Even if he is included this time, it now seems likely, approaching inevitable, that he will not appear in an England selection thereafter.

He has already retired from one-day international cricket, and admitted after his man of the match performance in the second Test against South Africa at Headingley that the Lord's Test may be his last. If he really does want to play a full Indian Premier League season for the Delhi Daredevils next year rather than missing the business end of the competition to appear in England's two-Test series against New Zealand that will precede the 2013 Ashes, then this has to be the end.

Miller has refused to be drawn on that, but did confirm that the off-field issues that have always swirled round Pietersen – most recently his startling complaints of isolation in the dressing room after the Headingley Test, and now the texts – have been considered. "A lot has been written and said this week and of course we've talked about these matters," the national selector said. "Bearing all this in mind, ultimately it's our job to pick the team we think is capable of winning the Test at Lord's and drawing the series. That's what we have to do."

Any other tricky decisions about the make-up of England's team for Lord's can be deferred until nearer to the start of the match. Graeme Swann, having been omitted at Headingley, is expected to return after taking his first three first-class wickets since May in a rare County Championship appearance for Nottinghamshire against Somerset in Taunton – presumably in place of either Tim Bresnan or Steve Finn, assuming there has been no Damascene conversion to the idea of playing a fifth specialist bowler.

Jonny Bairstow made an excellent 139 for the England Lions as their four-day match against Australia A at Old Trafford ended in a draw, his second century in five innings confirming the return of the Yorkshireman's confidence and form after he failed to establish himself in England's problem No6 position during the series against West Indies earlier this summer. But even with Ravi Bopara still unavailable for personal reasons, Bairstow's chances of a recall would seem to have been scuppered by James Taylor's promising Test debut at Headingley. Unless, of course, an unexpected vacancy has emerged at No4.